The ministry stressed that all nuclear weapons in Russia have been under reliable protection since the 1991 Soviet collapse — despite the nation's economic turmoil.

"Despite all the difficulties our country faced in the beginning of the 1990s, standards of security and physical protection of Russian nuclear arsenals remained high," the ministry said in a statement. "There have been no 'leaks' of nuclear weapons."

The angry statement reflected a growing chill in Russia-U.S. ties badly strained over U.S. missile defense plans, Russia's war in Georgia in August and other issues.

Gates spoke earlier this week at the Carnegie Endowment for International Peace in Washington, expressing worries that some Russian nuclear weapons from the old Soviet arsenal may not be fully accounted for.

"I have fairly high confidence that no strategic or modern tactical nuclear weapons have leaked" beyond Russian borders, Gates said. "What worries me are the tens of thousands of old nuclear mines, nuclear artillery shells and so on, because the reality is the Russians themselves probably don't have any idea how many of those they have or, potentially, where they are."

The allegations and angry refutations unfortunately come on the heels of the successful completion of the largest secure shipment of highly enriched uranium from former Soviet satellite states back to Russia for safekeeping. And it was the United States the coordinated the secret transport of weapons-grade uranium to its former Cold War enemy.